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cd24f44050
csr_sscratch CSR holds current task_struct address when hart is in user space. Trap handler on entry spills csr_sscratch into "tp" (x2) register and zeroes out csr_sscratch CSR. Trap handler on exit reloads "tp" with expected user mode value and place current task_struct address again in csr_sscratch CSR. This patch assumes "tp" is pointing to task_struct. If value in csr_sscratch is numerically greater than "tp" then it assumes csr_sscratch is correct address of current task_struct. This logic holds when - hart is in user space, "tp" will be less than csr_sscratch. - hart is in kernel space but not in trap handler, "tp" will be more than csr_sscratch (csr_sscratch being equal to 0). - hart is executing trap handler - "tp" is still pointing to user mode but csr_sscratch contains ptr to task_struct. Thus numerically higher. - "tp" is pointing to task_struct but csr_sscratch now contains either 0 or numerically smaller value (transiently holds user mode tp) Link: https://lkml.kernel.org/r/20231026233837.612405-1-debug@rivosinc.com Signed-off-by: Deepak Gupta <debug@rivosinc.com> Reviewed-by: Andrew Jones <ajones@ventanamicro.com> Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com> Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Tested-by: Hsieh-Tseng Shen <woodrow.shen@sifive.com> Cc: Albert Ou <aou@eecs.berkeley.edu> Cc: Glenn Washburn <development@efficientek.com> Cc: Jan Kiszka <jan.kiszka@siemens.com> Cc: Jeff Xie <xiehuan09@gmail.com> Cc: Kieran Bingham <kbingham@kernel.org> Cc: Palmer Dabbelt <palmer@rivosinc.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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vmlinux-gdb.py |